A known parking assist system for automatically guiding a vehicle to a target parking position estimates a present vehicle position based on each wheel speed detected by a wheel speed sensor, and a yaw rate detected by a yaw rate sensor during the implementation of the parking assist control. In case that the present vehicle position is deviated from a target locus, a wheel steering angle is corrected in response to the deviation amount from the target locus, thereby correcting the deviation from the target locus. Such a parking assist system is disclosed in Japanese Patent Laid-Open Publication No. H10-264839. According to the disclosed parking assist system, when the estimated present vehicle position is deviated from the target locus, the present position being deviated can be corrected without resetting the target locus.
According to the known parking assist system including the above disclosed parking assist system, however, the present vehicle position monitored during the implementation of the parking assist control is an estimated value based on information from the yaw rate sensor, the wheel speed sensor, and the like. Therefore, when a system error such as a malfunction of the yaw rate sensor occurs, the system may wrongly recognize that the present vehicle position is on the target locus despite the fact that the estimated present vehicle position and the actual vehicle position are different from each other. In this case, the parking assist control is continued as long as the system error is not detected and thus the vehicle may be guided to an in appropriate position different from the target parking position.
Thus, a need exists for a parking assist apparatus that can detect a system error thereof and improve reliability.